ELECTRICAL MEASUREMENTS OF SKIN IN VIVO.' II 423 C. ELECTRICAL MEASUREMENTS IN EXPERIMENTALLY INDUCED DRY SKIN Using glass cylinders affixed to the arms with elastic bands, the inner forearms were dried by either extracting with a solvent (acetone-ethanol, 1/1 V/V) for five minutes or by daily 30-minute exposures to a 30% aqueous solution of Sodium Lauryl Sulfate (SLS). Measurements were taken from these areas and from adjacent control sites using the wire-mesh electrode first and then the wet electrode. D. EFFECT OF MOISTURIZER ON SKIN HYDRATION Human volunteers were instructed to wash their forearms, during the week preceding the test, at least once a day using Ivory © or Camay © brand soap. During this period, the subjects were not permitted to use any topical products on their forearms. In the morning of testing, circular areas on the inner forearms were delineated using a fine-point permanent marker (Figure 2). Aliquots of 6 _+ 0.2 mg. of test samples, Figure 2. Test sites outlined with black ink on inner forearm. measured with a micropipette, were uniformly spread over the test area using the tip of a thin fire-polished glass rod. After sample application, the subjects were kept idle in an air conditioned room (45% R.H.) with their arms exposed. After 90 minutes of equilibration, electrical measurements were taken with the wire-mesh electrode periodically over 7.5 hours. In some experiments, measurements were taken about 18 hours after test sample application. Following this operation, the forearms were thoroughly washed with soap and lukewarm water with gentle rubbing with a sponge. In order to be able to locate the test sites, the marks were renewed some time before washing. After allowing the skin to dry for at least two hours, the electrical measurements were repeated. The objective of these experiments was to determine if moisturizers retained any activity after the sites treated with them were washed. E. PRINCIPAL LOTION INGREDIENTS The lotions used in these studies contain the following ingredients in order of decreasing concentration as well as other ingredients in lower concentrations: Lotion A--Water, mineral oil, potassium stearate, sodium stearate, cholesterol, and cetyl palmitate. Lotion B--Water, glyceryl stearate plus sodium lauryl sulfate, stearyl heptanoate, cyclomethicone, and glycerine. Lotion C--Water, diisopropyl sebacate, glyceryl monostearate, cetyl alcohol, and glycerine. Lotion D--Water, glycerine, and mineral oil.

424 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS RESULTS AND DISCUSSION A. ELECTRODE EFFECTS ON SKIN MOISTURE LEVELS Changes in skin hydration occurring while taking electrical measurements have been a matter of concern for many investigators (3, 5, 7). Such changes are caused mainly by transfer of electrolyte-moisture to the skin and by accumulation of water from insensible perspiration under the electrode. For these reasons we conducted experi- ments to determine the extent to which the use of the wire-mesh electrode (Figure 1) might affect skin moisture. The experimental design used for this purpose permitted us to compare results with this electrode to measurements with an electrode filled with a potassium chloride electrolyte cream and to determine if repeated application of the wire-mesh electrode at short time intervals would have a cummulative effect on water in the stratum corneum. Conductance and capacitance measurements taken with the wire-mesh electrode SOLVENT DRIED SITE A SITE B 0.15 r • [ 0.00 WET ELECTRODE -0.12 log E/C -0.25 -0.39 DRY ELECTRODE 0.30 0.00 log E/C -0.30 -0.6O -O.90 DETERGENT DRIED SLS t t SLS SLS I 2 DAYS WET ELECTRODE DRY ELECTRODE Figure 3. Conductance [777--• and capacitance • measurements in skin after extraction with acetone-ethanol (1/1, v/v) for 5 min or 30 min daily exposure to a 30% aqueous solution of sodium lauryl sulfate (SLS). The points on the graphs represent logarithmic values of the ratio of extracted (E) to adjacent control (C) skin sites. The measurements in the solvent-exposed skin were taken 5 rain after solvent removal followed by drying in air. In the SLS exposed skin the measurements w.ere taken after removing the SLS solution by washing with soap and water and subsequent drying for at least 2 hours.